Apparatus for controlling chucking pressures on workpieces in machine tools

ABSTRACT

The present invention provides a method of and apparatus for controlling chucking pressures on workpieces in machine tools carrying out machining operations by chucking the widths, outer surfaces or inner surfaces of workpieces with hydraulic pressure, magnetic forces or mechanical force, the principal arrangement thereof being such that in order that the internal stresses in a workpiece may be dissipated or relieved in accordance with changes in the cutting speed in an automatic working cycle thereby to improve the accuracy of finishing, the chucking pressures are properly adjusted. It also provides methods of and apparatuses for controlling chucking pressures on workpieces in machine tools, having sub-arrangements based on said principal arrangement. Advantages and details of such arrangements will be made clear.

United States Patent [191 Hiramatu et al.

[ 1 Nov. 13, 1973 APPARATUS FOR CONTROLLING CHUCKING PRESSURES ONWORKPIECES IN MACHINE TOOLS [75] lnventors: Sadakazu Hiramatu; TomoyosiEgusa; l-Iiromiti Tateisi, all of Iwata, Japan I [73] Assignee: ToyoBearing Manufacturing Company Limited, Osaka-shi, Japan [22] Filed: May5, 1971 [21] Appl. No.: 140,368

[30] Foreign Application Priority Data Dec. 5, 1970 Japan" 45/107804[52] US. Cl 279/4, 91/31, 91/32, 51/290, 82/] C, 82/30 [51] Int. Cl B23b31/30, Fl5b 31/04 [58] Field of Search 279/4; 51/290; 91/31, 32; 82/1 C,30

[56] References Cited UNITED STATES PATENTS 3,091,256 5/1963 Becker279/4 X 2,731,952 1/1956 Szabo 91/31 Primary Examiner-Francis S. HusarAttorney-Hall & Houghton [57] ABSTRACT The present invention provides amethod of and apparatus for controlling chucking pressures on workpiecesin machine tools carrying out machining operations by chucking thewidths, outer surfaces or inner surfaces of workpieces with hydraulicpressure, magnetic forces or mechanical force, the principal arrangementthereof being such that in order that the internal stresses in aworkpiece may be dissipated or relieved in accordance with changes inthe cutting speed in an automatic working cycle thereby to improve theaccuracy of finishing, the chucking pressures are properly adjusted. Italso provides methods of and apparatuses for controlling chuckingpressures on workpieces in machine tools, having sub-arrangements basedon said principal arrangement. Advantages and details of sucharrangements will be made clear.

1 Claim, 10 Dra vving Figures PAIENTEU HV 3 I915 3.771.802

SHEET 2 or 2 APPARATUS FOR CONTROLLING CHUCKING PRESSURES ON WORKPIECESIN MACHINE TOOLS BACKGROUND OF THE INVENTION a. Field of the InventionThe present invention relates to a method of and apparatus forcontrolling chucking pressures on workpieces in machine tools.

b. Field of the Prior Art In machine tools which carry out machiningoperations by chucking the outer diameters, inner diameters or widths ofannular workpieces with hydraulic pressure, pneumatic pressure or magnetpressure, e. g., internal grinders, if machining under heavy cuttingload, i. e., rough grinding is to be effected, it is necessary to chuckthe workpiece with a sufficiently strong chucking pressure to withstandit. Chucking of the workpiece with a high chucking pressure, however,produces internal stresses in the workpieces. Besides this, duringmachining operation, additional internal stresses due to machining willbe produced. Therefore, if 'such high chucking pressure is maintaineduntil the completion of machining, upon removal of the workpiece saidinternal stresses will appear in the form of the deformation,contraction or expansion of the workpiece.

Machine tools of this type which are now on the market are designed tochuck workpieces with a constant chucking pressure, as seen in FIGS. 1and 2. This will now be described in more detail with reference to FIGS.1 and 2.

Supposing that a machined workpiece is released at t,, the chuckingpressure naturally becomes zero. After the lapse of a predeterminedperiod of time, a fresh workpiece is chucked at whereupon the chuckingpressure becomes P During t t,,, a grinding wheel or cutter is quicklyapplied to the workpiece, followed by rough machining during t t finishmachining during t,, t sparking out during t t quick withdrawal of thegrinding wheel or cutter during t, i and, after the lapse of apredetermined period of time from t,,, release of the workpiece at Thus,the chucking pressure is maintained constant at-P, from the time theworkpiece is chucked at until the time it is released at t,,

In short, since said machine tools now on the market chuck a workpiecewith a coristant pressure throughout the cycle as described above, whenfinish machining is operated after heavy duty machining (grinding),internal stresses naturally remain in the workpiece, causing thedrawback that the accuracy of machining is low.

SUMMARY OF THE INVENTION The present invention depends on chuckingduring rough machining operation a workpiece with a high pressuresuitable for rough machining, and then switching the chucking pressureover to a low pressure suitable for finish machining at the same time'asrough machining is completed, so that the internal stresses producedduring rough machining and the internal stresses due to the highpressure are dissipated or relieved, in which condition finish machiningis operated thereby improving the final accuracy of the workpiece, andprovides improved apparatus for so doing as well as an improved processfor so doing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a working cycle diagram foran annular workpiece working machine (grinder). FIG. 2 is a conventionalchucking pressure diagram in said cycle. FIGS. 3, 5, 6, 7 and 9 arechucking pressure diagrams in said cycle for machine tools (grinders)according to the present inventionv FIGS. 4, 8 and 10 are diagrams ofapparatus embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relatesto a method of and apparatus for controlling chucking pressurescharacterized by adjusting chucking pressures in accordance with changesin cutting speed in an automatic working cycle.

FIG. 3 shows a method of controlling chuckling pressures by apparatus ofthe invention. In this method, during rough machining, the chuckingpressure is P and upon completion of rough machining it is lowered to Pwhich is maintained until release of the workpiece, during which timefinish machining is operated.

The above-mentioned chucking pressure may be applied in any desiredform, such as fluid pressure, electromagnetic force and mechanicalforce.

An example in which fluid pressure is utilized will now be described.

In FIG. 4, the numeral 1 denotes a chuck pressure changeover valve; 2, achuck cylinder; 3 and 4, pressure-reducing throttling valves; 5, apressure gauge; and the numeral 6 denotes a main line. In this circuit,when fluid is fed to the main line and the chuck pressure changeovervalve 1 is opened, the primary line becomes maintained at set pressure,i. e., a chuck pressure P, suitable for rough machining, by means of thepressure-reducing throttling valve 4 disposed in the main line 6 andthis fluid pressure acts on the chuck cylinder 2. Naturally, thenceforththe chuck pressure is maintained at P In this condition, rough machiningis operated. At the same time as rough machining is completed, the chuckpressure changeover valve 1 is closed. Thenceforth, the fluid flowsthrough the pressure-reducing throttle valve 3 disposed in a branch line7 and then flows into the main line6. Therefore, the secondary side ofthe pressure-reducing throttling valve 3 becomes maintained at Psuitable for finish machining by means of the pressure-reducingthrottling valve 3. Thenceforth said pressure is maintained at P untilthe flow in the main line 6 is interrupted.

FIGS. 5 through 7 show other embodiments of 'the method of controllingchucking pressures by apparatus of the present invention, wherein at thesame time as rough machining is completed, the chucking pressure isgradually lowered to P and finish machining is operated at this chuckpressure P,.

That is, this method is an improvement on the first method describedabove; In the first method, at the same time as rough machining iscompleted, the chuck pressure P, is quickly lowered to the finish chuckpressure P With this, however, in the case of an annular workpiece,there is a danger of causing misalignment. If misalignment occurs, theworkpiece could collide with the grinding-wheel or cutter. It is thissecond method that has overcome such drawback.

The chuck pressure in said second method may be in any desired form,such as fluid pressure, electromagnetic force and mechanical force.

In embodying the second method, an example in which fluid pressure isutilized will now be described with reference to FIG. 8.

FIG. 8 is an addition of an accumulator 8 to the main line 6 between thebranch line 7 and chuck cylinder 2 in the circuit described inconnection with the first method, the rest of the arrangement being thesame as in FIG. 4. In this circuit, when fluid is permitted to flow inthe main line 6 and the chuck pressure changeover valve 1 is opened, thesupplied fluid passes through the chuck pressure changeover valve 1 andreaches the chuck cylinder 2. The pressure at this time is the pressureP, suitable for rough machining set by the pressure-reducing throttlingvalve 4.

When the chuck pressure changeover valve 1 is opened, part of the fluidflowing through the main line 6 is stored in the accumulater 8. That is,a fluid pressure corresponding to the pressure P, is stored in theaccumulator 8 by pushing up a piston against the force of a spring 9. Inthis condition, if the chuck pressure changeover valve 1 is closed uponcompletion of rough machining, the fluid passes not through the chuckpressure changeover valve 1 but through the pressurereducing throttlingvalve 3 in the branch line 7 and is then exhausted through the otherpressurereducing throttling valve 4. However, the closing of the chuckpressure changeover valve 1 causes the fluid stored in the accumulator 8to be discharged to the main line 6. The process of this discharge isshown in FIGS. 5, 6 and 7 wherein the pressure changes from P, to P,,that is, upon completion of rough machining the pressure is graduallylowered to P suitable for finish machining. This pressure change may bemade in the manner shown in FIG. 5, 6 or 7, as desired, by suitablydesigning the spring 9 housed in the accumulator.

A third method is used in cases where the strains in the annularworkpiece cannot be released except at pressure P which is lower thanthe chuck pressure P for finish machining. Thus, according to the thirdmethod, as shown in FIG. 9, upon completion of rough machining, thepressure is gradually lowered to P which is lower than the chuckpressure P suitable for finish machining and thereafter it is graduallyraised to the chuck pressure P,, at which finish machining is thenoperated. FIG. 10 shows an embodiment of the third method, which is amodification of the embodiment of the second method (FIG. 8), whereinthe chuck pressure changeover valve 1 is replaced by a threewaychangeover valve 11 and additional provision is made of a branch line 15having a pressure-reducing throttling valve 14, the rest of thearrangement being the same as in FIG. 8. In this circuit, when onesolenoid 12 of the three-way changeover valve 11 is actuated, thepressure in the chuck cylinder 2 becomes maintained at the pressure P,suitable for rough machining, as in the case of the first and secondmethods. In this case, the interior of the accumulator 8 is also at thepressure P,. Next, when the solenoid 12 is interrupted, the fluid passesthrough the pressure-reducing throttling valve 3 in the branch line 7and is exhausted through the other throttling valve 4. Simultaneouslytherewith, the fluid in the accumulator 8 is discharged, so that thepressure is gradually lowered until it reaches the pressure P which islower than the finish machining chuck pressure P When the pressurereaches P the other solenoid 13 is actuated to feed the main line 6 withfluid from both of the pressure-reducing throttling valves 3 and 14,whereby the pressure changes from P back to P Thereupon, finishmachining is operated at the desired finish chuck pressure P Whilesthere have been described herein what are at present considered preferedembodiments of the several features of the invention, it will be obviousto these skilled in the art that modifications and changes may be madewithout departing from the essence of the invention.

It is therefore to be understood that the exemplary embodiments thereofare illustrative and not restrictive of the invention, the scope ofwhich is defined in the appended claims and that all modifications thatcome within the meaning and range of equivalency of the claims areintended to be included therein.

We claim:

1. An apparatus for controlling chucking pressures on workpiecescomprising, in combination:

a. a pressure operated chuck cylinder,

b. a fluid pressure line connected thereto,

0. a source of fluid pressure,

d. a chuck pressure change-over valve connected between said source andsaid line and operable to admit fluid pressure from said source to saidline,

e. a pressure indicator connected to said line,

f. a first pressure-reducing throttling valve connected to said line forproviding throttled discharge of fluid pressure from said line forestablishing a first chucking pressure in said line when said changeovervalve is opened to admit fluid pressure from said source to said line,

g. means comprising a second pressure-reducing throttling valveconnected to said source and to said line in parallel with saidchange-over valve for supplying fluid at reduced pressure to said linefor establishing in said line with said first throttling valve a secondchucking pressure less than said first chucking pressure when saidchange-over valve is closed,

h. a pressure accumulator connected to said line for regulating the rateof pressure change therein when said change-over valve is closed, forinhibiting misalignment of the work thereby,

i. a third connection from said source to said line, said thirdconnection comprising in series therein a cut-off valve and a thirdthrottling valve, and

j. said first, second and third throttling valves andaccumulator-constituting means operable for causing the pressure in saidline to drop to a pressure lower than said reduced pressure when saidchange-over valve and cut-off valve are closed for relieving strains inthe work, and operable for causing the pressure in said line tothereafter rise to said reduced pressure when said cut-off valve isopened.

1. An apparatus for controlling chucking pressures on workpiecescomprising, in combination: a. a pressure operated chuck cylinder, b. afluid pressure line connected thereto, c. a source of fluid pressure, d.a chuck pressure change-over valve connected between said source andsaid line and operable to admit fluid pressure from said source to saidline, e. a pressure indicator connected to said line, f. a firstpressure-reducing throttling valve connected to said line for providingthrottled discharge of fluid pressure from said line for establishing afirst chucking pressure in said line when said change-over valve isopened to admit fluid pressure from said source to said line, g. meanscomprising a second pressure-reducing throttling valve connected to saidsource and to said line in parallel with said change-over valve forsupplying fluid at reduced pressure to said line for establishing insaid line with said first throttling valve a second chucking pressureless than said first chucking pressure when said change-over valve isclosed, h. a pressure accumulator connected to said line for regulatingthe rate of pressure change therein when said change-over valve isclosed, for inhibiting misalignment of the work thereby, i. a thirdconnection from said source to said line, said third connectioncomprising in series therein a cut-off valve and a third throttlingvalve, and j. said first, second and third throttling valves andaccumulator constituting means operable for causing the pressure in saidline to drop to a pressure lower than said reduced pressure when saidchange-over valve and cut-off valve are closed for relieving strains inthe work, and operable for causing the pressure in said line tothereafter rise to said reduced pressure when said cut-off valve isopened.